1. Field of the Invention
The present invention relates to a motor controller of an electric power steering device which is mounted in vehicles such as automobiles.
2. Related Art
As a required steering assist force is increased, an electric power steering device needs to flow a high current into a motor. Electric power may be insufficient if it is supplied only from an in-vehicle battery. Therefore, although electric power is supplied from the in-vehicle battery as a main power supply normally, a terminal voltage of the main power supply may decrease due to an increase in load. In such a case, conventionally, there has been proposed a configuration in which electric power is supplied from an auxiliary power supply, which has previously stored electric power, such that the burden of the main power supply is reduced. (See JP-A-2006-282121.) In case that the auxiliary power supply is used, a diode is inserted into an electric path such that a current does not flow into the electric power steering device from the main power supply.